Iodine → (6S)-5,6,7,8-tetrahydrofolic acid

Participants

Reaction Conditions

Reaction Steps

A solution of crude XVIb (1.34 mmol) in 30 mL 0.01M HCl was cooled to 18° C., and 33 mL of 50 mM I2 in MeOH (1.65 mmol) was added over 10 s with good stirring, with a consequent increase in temperature to 27° C. After 2.0 min, the mixture was cooled within 2.7 min to -20° C. This temperature was maintained during subsequent titration to pH 9.2 (measured without dilution) with 10M NaOH over a period of 1.5 min. The reaction was rapidly warmed to 0° C., and at the same time sparged vigorously with argon. After 3.0 min at 0° C., 58 mL of 0.1M Na2S2O4 (freshly dissolved in deaerated water) was added all at once with stirring, followed 2.0 min later by 0.82 mL 2-mercaptoethanol (11.7 mmol). Analysis by cation exchange HPLC indicated 0.74 mmol of tetrahydrofolic acid (55%). Contaminating impurities included small amounts of 7,8-dihydrofolic acid (XXIIIb), XIXb (λmax =290 nm, pH 3.0), PABA-glu, and trace N5,N10-methylene-tetrahydrofolic acid, with 74% of the 285 nm absorbance area located in the peak of desired product.

Provenance & Evidence